The present invention relates to devices for pumping molten metal. More particularly, the invention relates to a more efficient molten metal pump that includes low-maintenance, easy-to-replace components.
Devices for pumping molten metal (referred to herein as molten metal pumps or pumping devices), particularly molten aluminum, and various components that can be used with these devices are generally disclosed in U.S. Pat. No. 2,948,524 to Sweeney et al. and U.S. Pat. No. 5,203,681 to Cooper entitled xe2x80x9cSubmersible Molten Metal Pump,xe2x80x9d the disclosures of which are incorporated herein by reference.
A problem inherent in prior art devices is costly, time-consuming maintenance. Molten metal pumping devices operate in an extremely hostile environment, usually a molten aluminum bath. The molten aluminum is maintained at a temperature of 1200-1500xc2x0 F. and contains contaminants, such as magnesium, iron, dross and pieces of brick. Additionally, chlorine gas, which is highly corrosive, is usually released in the molten aluminum to react with and remove the magnesium. As a result of the high temperatures and chemical composition of the metallic bath, the bath is extremely caustic and gradually oxidizes the pumping device""s components.
Another problem with molten metal pumps is related to the pressure generated by pumping the metal and the presence of solid particles within the molten metal bath. Molten metal pumps include a motor, a rotor shaft, a rotor (or impeller) and a pump base. The pump base has a chamber formed therein, an input port(s) (also called an inlet(s)) and a discharge that leads to an output port (also called an outlet). The input port and discharge are in communication with the chamber. The motor is connected to the rotor shaft and drives, or spins, the rotor shaft, connected to the rotor, which is located within the pump chamber. The molten metal enters the chamber through the input port(s) and the spinning rotor forces (i.e., pumps) the molten metal through the discharge and out of the port.
The pressure generated by pumping the molten metal can cause the rotor shaft to move eccentrically (i.e. to wobble). Further, if solid particles such as slag or brick enter the pump chamber and strike the rotor, the rotor shaft is jarred. Eccentric movements and sudden changes in speed caused by jarring can damage the rotor shaft or the coupling that joins the rotor shaft to the motor drive shaft. In order to prevent the rotor shaft from breaking, and to prevent damage to the coupling, the coupling should be flexible to allow for movement.
Further, when dross, pieces of brick or other solid particles enter the pump chamber they may wedge between the rotor and the upper wall of the pump chamber, which may cause the rotor to jam and the rotor shaft to break. One solution to this problem is described in U.S. Pat. No. 5,203,681 to Cooper entitled xe2x80x9cSubmersible Molten Metal Pump.xe2x80x9d This patent discloses a pump having a non-volute pump chamber to allow for the passage of solids. Even if this design is utilized, however, solid particles may still wedge between the upper wall of the pump chamber, or upper wear ring, and the rotor, thus jamming the rotor.
Further, molten metal pumps come in several versions, one of which is referred to as a transfer pump. A transfer pump normally has a discharge formed in the top of the pump housing. A metal-transfer conduit, or riser, extends from the discharge and out of the metallic bath where it is generally supported by a metal support structure known as a superstructure and is connected to a 90xc2x0 elbow. The transfer pump pumps molten metal through the discharge and through the metal-transfer conduit and elbow where it exits into another metallic bath chamber (i.e., the molten metal is transferred to another chamber). Until now, the metal transfer conduit has been cemented to the discharge opening and to the steel superstructure. Although cementing the conduit generally works well, it is extremely difficult to replace a metal-transfer conduit so connected because: 1) the pump must be removed from the metallic bath and cooled, 2) the cement must be chiseled away, 3) the new conduit must be assembled and cemented to the discharge, 4) the conduit must be cemented to the steel supporting structure, and 5) the new cement must be cured to remove moisture, a process that, by itself, normally takes approximately twenty four hours. The entire replacement operation can take up to two days.
The present invention solves these and other problems by providing a molten metal pumping device comprising a molten metal pump including a rotor sized to fit within the pump chamber and to extend beyond the pump input port. As the rotor spins, the portion extending beyond the input port deflects many solid particles rather than allowing them to enter the pump chamber. This reduces the likelihood of jams occurring. Optionally, the rotor can be a dual-flow device. One embodiment of a dual-flow rotor of the present invention has substantially vertically-oriented vane(s) that have a top portion angled towards the horizontal axis. As the rotor spins, the angled top portion(s) direct the molten metal down into the pump chamber and the vertically-oriented portion(s) direct the molten metal outward against the wall of the pump chamber, where the metal is eventually directed out of the discharge.
The pumping device of the present invention also includes a novel coupling for connecting the rotor shaft to the motor drive shaft wherein the coupling comprises a first coupling member and a second coupling member with a flexible disk disposed therebetween. The first coupling member connects to the motor drive shaft and the second coupling member connects to the rotor shaft. If the rotor shaft moves eccentrically or is jarred, the flexible disk absorbs the movement, whether it be side-to-side or up-and-down, or a combination of both, in a full 360xc2x0 range, thus preventing the rotor shaft from breaking and preventing damage to the coupling or to the motor shaft. Furthermore, the coupling""s performance relies solely on the flexibility of the disk; it does not require lubricants to maintain its flexibility. Additionally, the coupling is not connected to either the motor drive shaft or rotor drive shaft by a threaded connection. It drives the rotor shaft by transferring force through coupling surfaces that mate with surfaces of the rotor shaft, which is described in greater detail herein.
The present invention also includes a pumping device comprising a transfer pump having a metal-transfer conduit that is not cemented or similarly affixed to the pump base or the steel superstructure. Preferably, the metal-transfer conduit has a first end configured to either rest on a button attached to the pump output port or to fit into an angled bore formed in the discharge. The metal-transfer conduit also has a second end opposite the first end that is supported by a two-piece coupling that engages the conduit without the use of cement or other sealant. With the noncemented structure of the present invention, it takes only a few hours to replace the metal-transfer conduit.
Further, any vertical member, such as the metal-transfer conduit, support posts or shaft, of the present invention can be provided as a plurality of connectable sections so that the section in contact with the extremely corrosive surface of the metallic bath may be individually replaced or be formed of highly corrosion-resistant material, such as ceramic; whereas the rest of the conduit may be formed of less expensive material, such as graphite. This structure also allows for the replacement of an individual worn section of a vertical member, instead of having to replace the entire member.
It is therefore an object of the present invention to provide a pumping device that increases pumping efficiency.
It is a further object of the present invention is to provide a device that includes a dual-flow rotor.
It is a further object of the present invention to reduce jamming that occurs in molten metal pumping devices.
It is a further object of the present invention to provide a pumping device that reduces maintenance downtime.
It is a further object of the present invention to provide a pumping device including a rotor shaft coupling that allows for eccentric movement and that does not require lubrication.
It is a further object of the present invention to provide a pumping device including a rotor shaft coupling that has no threads.
It is a further object of the present invention to provide a transfer pump including a metal-transfer conduit that is not cemented to the pump base.
It is a further object of the invention to provide a transfer pump as defined above wherein the metal-transfer conduit is supported by a pump superstructure without the use of cement.
It is a further object of the present invention to provide sectional vertical members including a sectional rotor drive shaft, sectional support posts and a sectional metal-transfer conduit wherein the sections can be connected with or without the use of cement or other sealants.
It is a further object of the present invention to provide a furnace thermocouple integral with the pump.
These and other objects will become apparent to those skilled in the art upon reading the following description and appended claims.